1. Field of the Invention
The present invention relates to a positive resist composition suitably used in the ultramicrolithography process of producing, for example, VLSI or high-capacity microchip or in other photofabrication processes. More specifically, the present invention relates to a positive photoresist capable of forming a highly refined pattern with use of electron beam, X-ray, EUV light or the like, that is, a positive resist composition suitably usable for fine processing of a semiconductor device, where electron beam, X-ray or EUV light (wavelength: around 13 nm) is used.
2. Background Art
In the process of producing a semiconductor device such as IC and LSI, fine processing by lithography using a resist composition has been conventionally performed. Recently, the integration degree of an integrated circuit is becoming higher and formation of an ultrafine pattern in the sub-micron or quarter-micron region is required. To cope with this requirement, the exposure wavelength also tends to become shorter, for example, from g line to i line or further to KrF excimer laser light. At present, development of lithography using electron beam, X ray or EUV light other than the excimer laser light is proceeding.
In particular, the electron beam lithography is positioned as a pattern forming technique of the next generation or second next generation and a high-sensitivity and high-resolution positive resist is being demanded. Among others, the elevation of sensitivity is a very important issue for shortening the wafer processing time, but in the positive resist for use with electron beam, when higher elevation is sought for, not only reduction of resolving power but also worsening of line edge roughness are brought about and development of a resist satisfying these properties at the same time is strongly demanded. The line edge roughness as used herein means that the edge of resist at the interface between the pattern and the substrate irregularly fluctuates in the direction perpendicular to the line direction due to the resist property and when the pattern is viewed from right above, the edge gives an uneven appearance. This unevenness is transferred in the etching step using the resist as a mask and causes deterioration of electric properties, giving rise to decrease in the yield. Particularly, in the ultrafine region of 0.25 μm or less, the improvement of line edge roughness is a very critical problem to be solved. High sensitivity, high resolution, good pattern profile and good line edge roughness are in a trade-off relationship, and it is very important how to satisfy these at the same time.
In the case of using EUV as a light source, the light is at a wavelength belonging to an extreme ultraviolet region and has a high energy and therefore, in corporation with a photochemical reaction such as negative conversion ascribable to EUV light, there arises a problem such as reduction of contrast. Accordingly, also in the lithography using X-ray or EUV light, an important issue is to satisfy high sensitivity as well as high resolution and the like at the same time. These problems are in need of resolution.
As for the resist suitable for such a lithography process using electron beam, X-ray or EUV light, a chemical amplification-type resist utilizing an acid catalytic reaction is mainly used from the standpoint of elevating the sensitivity and in the case of a positive resist, a chemical amplification-type resist composition mainly comprising an acid generator and a phenolic polymer which is insoluble or sparingly soluble in an alkali developer but becomes soluble in an alkali developer under the action of an acid (hereinafter simply referred to as a “phenolic acid-decomposable resin”) is being effectively used.
With respect to this positive resist for use with electron beam, X-ray or EUV, some resist compositions which are variously designed, for example, formulated to contain a phenolic acid-decomposable resin, have been heretofore known (see, for example, Patent Documents 1 to 9: JP-A-2002-323768 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-6-41221, Japanese Patent No. 3,173,368, JP-A-2000-122291, JP-A-2001-114825, JP-A-2001-206917, U.S. Pat. No. 5,558,978, JP-A-2002-202610, and JP-A-2000-241976, respectively).
However, it is impossible at present for any combination of these techniques to satisfy high sensitivity, high resolution, good line edge roughness and good pattern profile in an ultrafine region at the same time.